Problems of the start-stop system: symptoms, cost and affected models
We have documented 9 faults of the start-stop system in 1 engine and 8 cars, affecting 13 models of car in our database. The most important by severity and frequency: original battery that wears out early and low voltage with Start&Stop in the MiTo (Alfa Romeo MiTo), infotainment system faults and electronic warnings (screen, Start&Stop, alternator) (Fiat 500X) and weak battery that stops the Start-Stop system from working (Mercedes-Benz Clase C W205).
How it works and why it fails
Start-stop system
The start-stop system switches the engine off at stops and restarts it when you release the brake or press the clutch. It needs a special battery (EFB or AGM), a reinforced starter motor and several sensors, and it switches itself off if any of them is not in good condition.
What to do
Start-stop cutting out is usually a safeguard: the battery is low, the cabin needs climate control or the engine is not warm. If it never works again, check the battery and its sensor; when replacing the battery, use one of the same type and register it with the ECU if the car requires it.
General explanation by MotorFiable. The specific faults of each engine and car, with their sources, are on the linked pages.
Common symptoms
The symptoms that come up most often in the documented faults of the start-stop system. Open each one to see what other faults cause it.
Problems of the start-stop system by engine
From most to least important (severity × frequency). Each page details the affected versions and years, symptoms, cost and how to check for it.
Problems of the start-stop system by car
Faults documented on specific cars, which occur with any engine. From most to least important.
- 1Medium severityFrequency: OccasionalAlfa Romeo MiToOriginal battery that wears out early and low voltage with Start&Stop in the MiTo22 of the 297 reports on fiches-auto.fr mention the battery: fast discharge, low voltage affecting the Start&Stop and batteries replaced at 30,000 to 70,000 km, one of them "HS" at 40,000 km. One owner calls it underpowered from new. There is no official campaign.
- 2Medium severityFrequency: OccasionalFiat 500XInfotainment system faults and electronic warnings (screen, Start&Stop, alternator)Yes: several reports document infotainment system faults (frozen screen, FM radio, weeks in the garage to resolve it), Start&Stop system faults and diagnostic confusion between a battery fault and an alternator fault.
- 3Medium severityFrequency: OccasionalMercedes-Benz Clase C W205Weak battery that stops the Start-Stop system from workingA German used-car test points out that weak batteries are a known problem on the C-Class W205: when they lose capacity, the Start-Stop system stops working and, in the worst case, the car can end up immobilised.
- 4Medium severityFrequency: RareFiat Panda III12 V battery discharge and Start&Stop system faultsTestimonies from Fiat Panda III owners describe premature 12 V battery discharge and a Start&Stop system that in several cases stops activating; there is no official campaign or specialist press to confirm it.
- 5Medium severityFrequency: RareSuzuki IgnisWeak alternator-starter belt and start-stop faultOn the first Ignis (model year 2016, petrol units with a mild hybrid system), Suzuki found two defects: a start-stop fault that could prevent the battery from charging, and a belt without enough grip that could break. They were corrected through campaigns.
- 6Low severityFrequency: OccasionalFord Focus IIIThe Start-Stop system does not restart the engine automaticallySome Focus III owners with the automatic start-stop system (Start-Stop) notice that it does not always restart the engine when they release the brake. Auto Express points out that this is usually down to a battery that is starting to fail, not a fault in the system itself.
- 7Low severityFrequency: RareVolvo V60 IIWeak 12 V auxiliary battery that destabilises the electronics and Start-StopAccording to the reports collected by fiches-auto.fr, the 12 V auxiliary battery can cause Start-Stop faults and false warnings from the V60's monitoring system; in one specific case, a D4 190 hp had a fault after the battery was replaced and it was resolved under warranty.
- 8Low severityFrequency: RareVolvo V90Auxiliary Start-Stop battery worn out after six yearsA 2017 V90 D4 AWD needed its Start-Stop battery replaced at 150,000 km and around six years, according to the fiches-auto.fr page; the owner considers it normal wear. It is a single report on the page.
Problems of the start-stop system by make
Problems of the start-stop system in your car
3 cars have several documented faults of the start-stop system. Choose yours to see only the ones that affect them, by engine and by year.
Alfa Romeo 1
Fiat 2
Frequently asked questions
Which engines have the most faults of the start-stop system?
By severity and frequency, the 0.9 TwinAir and 1.0/1.3 FireFly (Start&Stop system faults, low severity).
Which cars have problems of the start-stop system?
Among those we have analysed: Alfa Romeo MiTo (original battery that wears out early and low voltage with Start&Stop in the MiTo), Fiat 500X (infotainment system faults and electronic warnings (screen, Start&Stop, alternator)), Mercedes-Benz Clase C W205 (weak battery that stops the Start-Stop system from working), Fiat Panda III (12 V battery discharge and Start&Stop system faults), Suzuki Ignis (weak alternator-starter belt and start-stop fault), Ford Focus III (the Start-Stop system does not restart the engine automatically), Volvo V60 II (weak 12 V auxiliary battery that destabilises the electronics and Start-Stop) and Volvo V90 (auxiliary Start-Stop battery worn out after six years).
What symptoms does a fault of the start-stop system cause?
The most frequently cited in the documented faults: battery goes flat while the car is parked, intermittent electronic warnings or sensor faults, heavy steering or power steering warning, screen or infotainment system freezes or restarts and battery warning light on.